Historically, oil analysis was an off-site strategy handled by commercial laboratories. However, oil analysis has recently been viewed as a tool for managing a core asset, and on-site oil analysis has experienced rapid growth in many industrial fields.
As technology has advanced, more low-priced sensors have been introduced in the market. The purpose of these sensors is to measure the conditions of a machine in real-time and to provide analysts with highly reliable detailed information on the service life of the machine. However, analysis techniques using such sensors usually only measure a single parameter. Also, such techniques require use of the same lubricant or assume no machinery malfunctions during the measurement of a single parameter. As a result, such single-parameter sensors merely provide a narrow view on quality and/or health of a lubricant. However, it is virtually impossible to assess accurate lubricant health and to predict service intervals therefore by sensing a single parameter of the lubricant. Accordingly, to unambiguously identify any damage to the machine or the deteriorated state of the oil, it is important to measure a set of as many different parameters as possible. An integrated monitoring system may provide estimation of oil conditions/contamination and wear particle contents of oil in real time. Such a system may have directly built-in oil circulation lines of a machine or may be used like portable detectors in fields and laboratories. To monitor critical and expensive equipment, diagnostics based on standard oil parameters is needed in a number of cases.
In this regard, U.S. Pat. No. 6,561,010 describes a machine fluid analysis system that measures oil parameters similar to those obtained by standard laboratory machine fluid analysis. The system includes a viscometer (for viscosity), an energy dispersive X-ray fluorescence (EDXRF) spectrometer utilizing isotopic or X-ray tube X-ray sources (for elemental analysis), non-dispersive IR/visible light meter (for oxidation, nitration and turbidity). Analyzed oil is fed from monitored equipment through oil line/pipe to the system. The oil passes through a cooler before feeding into the EDXRF. Measurement of viscosity provides an indication of possible dilution of the oil by fuel or water. Viscosity can also indicate oil degradation from heat or oxidation. Chemical degradation of the oil (oxidation, nitration, etc.) is commonly determined by IR spectrometric analysis, as well as TAN and TBN analyses for the oil. Water in the oil is also detected by IR analysis. Slow coolant leaks into the lubricating oil system may be detected by EDXRF analysis of Boron, Chromium or other elements such as Iodine or Strontium added to the coolant water as salts. A controller that includes a microprocessor, memory, digital input/output, analog input, and mass storage, is used for controlling the system and collecting measured data. A modem is used to make on-board in situ information available to a remote observer of machine health. The system can provide a reliable conclusion to health condition of machine. However, due to its complexity and high price, the system is rather restrictively employed and may only be justified for monitoring critical industry equipment.
Further, as a state-of-the-art technology, modular systems with low cost sensors, which are sensitive elements integrated on a single substrate, have been developed. For example, U.S. Pat. No. 6,286,363 and U.S. Patent Application Publication No. 2005-0072217 describe a modular lubrication sensor, which is made using integrated circuit-like microfabrication techniques (silicon-based fabrication and deposition techniques). The lubrication sensor includes a semiconductor silicon base, on which a pH sensor, a chemical sensor, an electrical conductivity sensor and a temperature sensor are deposited. The pH sensor includes a reference electrode made of AgCl and a pH electrode made of palladium-palladium oxide (Pd—PdO). The chemical sensor is of a 3-electrode configuration, which includes a working electrode made of Ag, a reference electrode made of AgCl, and a counter electrode made of Ag. When either an AC or DC voltammetric signal is applied to the working electrode, a response current is generated between the working electrode and the counter electrode. The response current signal parameters vary depending upon the electrochemical processes occurring at the surface of the working electrode. The electrochemical processes are a function of the constituent concentrations, and the response current is therefore responsive to these concentrations. The electrochemical sensor determines the presence of water or oxidation in the lubricant. The electrical conductivity sensor consists of two electrodes and made of gold. The conductivity is used to determine metal wear and/or water present in the lubricant. The temperature sensor is platinum zone patterned on the base in accordance with a predetermined length, width and surface area.
Other modular sensors, which use a similar integrated circuit technology, are available in the market, but their reliability is rather low.
Consequently, there remains a strong need to develop reliable sensors, which provide adequate information and diagnostic capability, in order to develop modular systems with multi-function outputs.